The embodiments described herein relate generally to operating a power converter, and more specifically, to applying a nonlinear tracking filter within a current regulator of the power converter.
Light and wind are examples of renewable sources of energy that are increasingly becoming attractive alternative sources of energy. Solar energy in the form of sunlight may be converted to electrical energy by solar cells. A more general term for devices that convert light to electrical energy is “photovoltaic cells.” Wind energy may be converted to electrical energy using a wind turbine generator. Wind turbine generators typically include a rotor having multiple blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive an electric generator.
Power generated by an electric utility, using renewable sources of energy or fossil fuel based sources of energy, is typically delivered to a customer over an electrical grid. Electricity applied to the electrical grid is required to meet grid connectivity expectations. These requirements address safety issues as well as power quality concerns. For example, the grid connectivity expectations include operating the power generation system during a transient event, also referred to herein as a grid fault event. This capability may be referred to as low voltage ride through (LVRT) or zero voltage ride through (ZVRT). An LVRT/ZVRT event is a condition where the alternating current (AC) utility voltage is low on either one phase of the electrical grid or multiple phases of the electrical grid. During an LVRT/ZVRT event, the capacity of the electrical grid to accept power from the power generation system is low, a condition also referred to herein as a “weak grid”.
To avoid adverse interaction between the converter and the electrical grid, the bandwidth of a current regulator included within known power converters is reduced. For example, known power converters include a current regulator that utilizes low-pass filtering to avoid adverse interaction between the converter and the electrical grid. The low-pass filtering may prevent high-frequency grid resonances affecting the electrical grid. However, the low-pass filtering (i.e., reduced bandwidth of the current regulator) slows the response of the converter and causes delays in a converter response to a grid fault event.
A slow response to a grid fault event may prevent the power converter from riding through the grid fault event. The power converter must rapidly respond to a grid fault event to ride through a low voltage or a zero voltage grid condition. More specifically, if the power converter does not respond quickly to the grid fault event, the voltages and/or currents at an output of the power converter may exceed protective thresholds. Exceeding the protective thresholds may cause the converter to trip, which prevents the converter from riding through the grid fault event.